1. Technical Field
The present disclosure relates to a semiconductor device.
2. Description of Related Art
As a form of a field effect transistor (FET), a high electron mobility transistor (HEMT) is widely used in the art because of its high electron mobility and low resistance. The key element within the HEMT is a heterojunction formed by two materials with different band gaps instead of a pn-junction used in the conventional FET. A commonly used material combination of the two materials of the heterojunction is AlGaN and GaN. Since the heterojunction created by AlGaN and GaN forms a quantum well in the conduction band on the GaN side, a two-dimensional electron gap (2DEG) appears at the interface of AlGaN and GaN.
An enhancement-mode FET (e.g. HEMT), which is normally off at zero gate-source voltage, is a switching element in a logic circuit. Conventional methods for manufacturing an enhancement-mode AlGaN/GaN HEMT include: (1) employing a thin AlGaN layer, (2) performing a gate-recess process, (3) using fluoride-based plasma treatment, (4) using oxygen plasma treatment, (5) employing a pn-junction gate, (6) employing a metal-insulator-semiconductor gate structure, and (7) employing an annealed Pt-based gate metal. However, the aforementioned methods have drawbacks of the threshold voltage being not easy to control and not spatially uniform, and/or damages may occur during surface processing in the manufacturing.